Neuropeptides may soon be used to treat neuropsychiatric diseases in man. However, brain cells are protected from the effects of circulating peptides by the brain endothelial wall, i.e., the blood-brain barrier (BBB). The available evidence indicates specific transport systems in the BBB, similar in nature to carrier systems known to transport nutrients and thyroid hormones, do not exist for peptides. There is evidence, however, that specific receptors for circulating peptides such as insulin do exist on the luminal side of brain endothelia. Peptide binding to the BBB may generate the production within endothelia of second messenger compounds that are released to brain extracellular space; in this way mechanisms would exist for the rapid modulation of brain cell function by circulating peptides, without the peptide actually crossing the BBB. Our studies propose to examine peptide binding and action at the BBB using the isolated cerebral capillary as the primary model system. Brain capillaries make up the BBB and these structures can be readily isolated in pure form from fresh bovine or rat brain. Three major areas will be investigated. The specific binding to isolated capillaries of such peptides as insulin, enkephalins, vasopressin, somatostatin, angiotensen II, and prolactin, will be studied with a radio-receptor assay. Secondly, the peptide-mediated release from isolated capillaries of such putative second messengers as cyclic AMP, cyclic GMP, glycine, glutamate, aspartate, or gaba, will be investigated using a silicone oil rapid separation technique, Thirdly, monoclonal antibodies to BBB peptide receptors will be raised by injecting isolated capillaries into mice and fusing mouse spleen cells with mouse myeloma cells to produce a hybridoma. The production of a monoclonal antibody will allow us to realize our long-term goals of isolating a specific BBB peptide receptor.